SCIENCE BRIEFING

Nitrous oxide, known as laughing gas, is the biggest man-made destroyer of Earth's ozone layer now that the use of chlorofluorocarbons and other ozone-depleting gases has been restricted globally.

Produced by fertilizing farmland and used by dentists to calm patients, nitrous oxide makes up about 40% of the emissions of ozone-depleting gases, said A.R. Ravishankara, a coauthor of a study in the journal Science.